Circuit boards are widely used to mechanically support and electrically connect electronic components. Circuit boards are generally rugged, inexpensive and can be highly reliable. Their dependable qualities have lead to their use in most electronic goods and in devices ranging from computers to lasers.
Circuit boards are generally placed in environments where the temperature will fluctuate. When its environment is hotter the circuit board will expand. Conversely, in colder environments the circuit board will contract. The degree to which the circuit board undergoes dimensional change in response to temperature is known as the Coefficient of Thermal Expansion (CTE).
Different materials have different CTE's and react to temperature changes differently. The degree to which a circuit board expands in hotter temperatures, will generally be different than that of its surrounding elements, including its housing. This can lead to relative movement between the circuit board and its housing. However in some cases the alignment between different components of a machine may be very important. For example in some applications, the center of the circuit board may need to be aligned with the center of the housing for optimal use.
Floating fasteners in conjunction with a fixed fastener were used in the past to prevent relative movement between a circuit board and its enclosure at a single point. The fixed fastener, such as a screw or a weld, was used at the single point to ensure that there was no relative movement at that location. Spacers (floating fasteners) were placed along other points to allow relative movement at other points.
Although floating fastener-based approaches to mounting circuit boards have been proven effective, they can only allow for coupling at the point of alignment such as the center of the circuit board and the housing. Floating fastener-based approaches do not allow for other coupling options at different points of the circuit board or housing. Furthermore when thermal expansion occurs, the circuit board and housing sometimes rub against each other and against the spacers which hold them apart. This rubbing can produce wear and contamination causing debris. This can damage the circuit board and hinder the performance of the overall device. The circuit board and housing also run the risk of sticking or binding together. This can lead to component or device distortion resulting in less than optimal use.